Magnetic focussing device for an electron tube



I nvenlor RYUZO ORU/ AGE NT July '5, 1,966 5 RYUZO ORUI v v MAGNETIC FOCUSSING DEVICE FOR AN ELECTRON TUBE F xed Jan. 8, "1962 s Sheets-Sheet 1 1 7 W m m M. W M A W H PM. H 1D VJ l W M M m W J U f u w W\\\\ v n11)! m MM u A MM m. m m v 52 Em QSEE Em BWZW 31( ndStc) iiiustmte granhicaily-athe magv v chic-field distribution of the device of FIG. 3(a). N flV C FDR FIG. 4 shows an alternative embodiment of the inven- .tional am pmt e njetie elements used in the invention.

Referring to FIG, l(a)-which shows schematically an axial section of a travelling-wave tube 1.0 with an immer cd field type magnetic focussing device; a uniform magnetic ,focussin-g d vice 1.1 is disposed around an electron gun 13 contained within .a glass envelope 12 of the travelling-wavetube, while a periodic magnetic focussing device 14 is disposed around the helix 15 thereof.

' The uniform magnetic tocussing device itself is, as shown in FIG. 2(a), composed of a cylindrical permanent magnet 17 with thin annular magnetic pole pieces 18'and 19 contiguous to both ends. Although in the drawing the cylindrical magnet 17 is shown as a single permanent magnet for the sake of simplicity, it may inciude a plurality 'of serially piled thin annular permanent magnets. The, axial distribution of the magnetic field produced by this device is shown by curve 20 of FIG. 2(b) ted-field t pe beam fo-. e" 9. wane c rc it inthe ma net t. Previqusf cus mp yet an 'fcrm n1. ,y

- sn th 9f the travel netic field (the positive partjof the ordinate corresponding to a right hand directed magnetic field) and the abscissa the distance along the axis. As is evident from portions adjacent the poles of the magnetic device 11,

counter magnetic fields (denotedby 21 and 22) whose field strengths are of the order of H as compared with t o he Positive magnetic field Hmmagnetic field along the. axis as shown by a dotted curve magnitude of the magnetic field (the positive part ofthe ordinate correspond ng to, the righthand directed magnetic ie d), and. the abscissa represents, the distance along the axis, It is assumed that at, the. line XX between the uniform magnetic focussirrg;v device 11 and the periodic magnetic focuss'ing device '14,, one pole of the former faces the same pole, of the latter and. that in the righthand Sid of the. line X-X the poles of "the cylindricahmagi we when t in e; s ch shie din ussi-ng the electron 14,, race pole o ik polarity.

When the. two tolcussing; devices are; used in conjunccnrve, 25; representing; the periodic, device and the dotdash. curv 22; re senting the; uniform! device are superposed: as shown; 16., 1-(1b:);.. The; resultantmagnetic field is. deno ed? bv- 2.63. As will: be evident from the foregoing; the simpiecomhination; of the uniform and the periodic; fjoonssi-rng devices) cannot; satisfactorily focus an elec, o n, beam, The resent; invention. intends toum a-ke he resultantimagne field-12.6;- nearly sinusoidal by varying; the, field; distrtibutr'om along; the; axis so as to; cancel the effec o he; leakage ma etic field 22'. In FIG; 3% which shows an embodiment: of" the th vel lingwavetube within: the; mag- :the; uniform; magnetic focussing ide; ofi the: line; are omitted a, to; the} corresponding portions sho nt El i; (a) elem nts ;constitutingathta peri- 31; .9 .133 andi t ole.- pieces 41; 42,, 43' interperiodic focus, trig; device 1114i as wellias; between-the: mag- 3 f,.3llt .3t magnitudeofjthemagnetic t field middle-H-Q ntstA, B 1 .t of 'thetrespectivetmag- 33; willinowbeconsideredt AliQOiniS gnor idNippDu 5. FIGS. 5 to 9 show modifications of the permanent magwherein the ordinate represents the magnitude of the una-g- 1 thi drawing, the leakage flux produces, at the outside Returning toFIG. 1(a) the periodic permanent focusd sing device 14 produces, a P riodical distribution of the 15' in FIG. 1( Here again the ordinate represents the nets, QO IY titn-tingthe periodic magnetic focussingt devicetion with one another as shown in. Fl Gt 1 ('a) the; dotted odic magnetic; fomssing .1345ampermanentrmagnets d; between th uniform; focussing device 1'1 and the.

theperiodicnnagneticfields'51;53555;,...

pole pieces 41, 42, 43

i the points A, B, C,

'most portion of the pole pieces 41, 42, 43,

v the extended portions 61, 63, 65,

, 3 (produced by the cylindricalmagnets 31, 33, 35, are of the same sense .is theleakage magnetic field 22 originating from the un form focussing device 11; hence the magnetic fields produced by these magnets may be of rather weak intensity. .The periodic magnetic fields 52, 5 4, 56, (produced by the cylindrical magnets 32, 34, 36 at the points B, D, F, on the other hand are of the reversed sense to the leakage magnetic field 22, and therefore, the magnetic fields produced by thesemagnets must be sufiiciently large to surmount the leakage magnetic field. Where cylindrical magnets 31,

32, 33, are designed to have equal magneto-motive force, the lengths of the axially extending portions of the are properly adjusted to vary the magnetic resistances and thus the magnetic fields at More particularly, the axial lengths of extended portions 61, 63, 65, at'the innerare made small so as to decrease the magnetic field along the axis at the middle points A, C, E, Inasmuch as the influence of the leakage magnetic field decreases with the order of the middle points A, C, E, the lengths of are increased in this order. Similarly, the lengths of the extended portions 62, 64, 66, are reducedwith the order of the middle points B, D, F, In this way quasi-periodic mag netic field 50 (defined by F (x) where F is a function of x,'the axial distance from line X-'-X)fhaving a varying amplitude as shown in FIG. 3( b) is obtained, which, when superposed on the leakage magnetic field 22 (defined as F (x) where F, is another function of x) results in a periodic magnetiefield 60 of constant amplitude as shown in FIG. 3(a). Although the pole pieces are shown to vary in width at the inner diameter they may similarly be varied at the outer diameter with the same effect.

FIG. 4 shows another embodiment of the invention wherein the size and thus the magnetic magnitude of the cylindrical magnets themselves is varied. Here, as may be seen, magnets 62, 64, 66, are of increasing intensity and size while magnets 61, .63, 65, are of decreasing intensity and size, so as to cause field d1stribution equivalent to that obtained by the embodiment of FIG. 3(a). Naturally in this embodiment, the pole pieces, while being constant in their axial extensions, vary radially to conform with the'size of the magnet.

Insteadof varying the size of the magnets the material of which they are composed may also be varied so as to varythe field intensity or remanence exhibited by each. Also, although the embodiment of FIG. 4shows a constant inner diameter, the outer diameter of the cylindrical magnets may remain fixed while the inner diameters are varied. r

Means for coupling into or out of the traveling wave tube may be inserted in the conventional manner without detracting fromthe invention. Yasud'as Patent No. 2,991,382 is illustrative. Since the requirement of the periodic .magnetic field at magnets 31, 33 is small such coupling means are preferably inserted there.

In the above described embodiments only cylindrical magnets are shown. These permanent magnets, however,

need not necessarily be cylindrical, but may be plate or bar magnets. FIGS. 5, 6 and 7 show a modification wherein plate magnets are used. A uniform magnetic device or an element of a periodic magnetic device is formed by disposing two plate magnets-71 and 72-above and below the tube 73 and attaching rectangular pole pieces 74, having a central circular'borei'such as shown in dr-ical surface whose center coincides with the tube axis;

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention, as set forth in the objects'thereof and in the accompanying claims.

What is claimed is:

1. A magnetic focussing system for a travelling wave tube including an electron gun region and a delay line region comprising:

a uniform magnetic device for producing a substantially uniform magnetic field axially threading said electron gun region of an inserted travelling wavetube, said device having an inherent leakage magnetic field;

a periodic magnetic device encircling the delay line region of said tube, having a sequence of successively oppositely directed annular permanent magnets of equal magnetic strength and radial pole pieces arranged between respective pairs of neighboring of said magnets, each of said pole pieces having an annular axial segment, said segments being of substantially equal length and being fixedly positioned relative to said pole pieces to provide different axial separations between adjacent successive pairs of said axial segments such that the magnetic effect of magnets having magnetic fields opposed to said leakage flux will be increased and the magnetic effect of magnets having magnetic fields -in coincidence with" said leakage magneticfield will be decreased, the difference in said separation 'between adjacent successive pairs of segments decreasing with distance from said uniform magnetic device to compensate substantially for the effects of said inherent leakage magnetic field on said periodic magnetic field.

2. A magnetic focussing system for a travelling wave and pole pieces arranged between respective pairs of neighboring said magnets, each of said pole pieces having an annular axial segment, the axial spacing between said axial segments of said pole pieces being substantially uniform, the magnetic field strengths of successive magnets being of increasing and decreasing magnetic intensity-so as to increase the magnetic effect of magnets having fields opposed to said leakage magnetic field and decrease the magnetic effect of magnets having magnetic fields in coincidence with said leakage magnetic field in a decreasing amplitude with distance from said uniform magnetic device, to compensate substantially for the effects of said inherent leakage magnetic field on said periodic magnetic field. E 3. A magnetic focussing system for a travelling wave tube includingan-electron gun region and a delay-line region comprising:

a uniform magnetic device for producing a substantially uniform magnetic field axially threading said electron gun region of an inserted travelling wave tube,

the inner and outer diameter of said permanent magnets being varied so as to increase'the magnetic effect of magnets having fields opposed to said leakage magnetic field anddecreasethemagnetic efiect of magnets having magnetic fields in coincidence I with said leakage magnetic field in a decreasing amplitude with distance from said uniform magnetic device, to compensate substantially for the eifects of 1 said inherent leakage'magnetic field on said periodic magnetic field.

4. A magnetic focussing system for a travelling wave tube including an electron gun region and a delay line region comprising: 5 I v a uniform magnetic device for producing a substantially uniform magnetic field axially threading said electron gun region of an inserted travelling wave tube,

said device having an inherent leakage magnetic a periodic magnetic device encircling the delay line region of said tube, having at least two successively 7 oppositely directed bar permanent magnets; and rectangular pole pieces arranged between respective pairs of neighboring said magnets, each of said polepieces having an annular axial segment;

5 s. CHATMON, 111., Assistant Examiner.

the inner and outer diameters of said bar permanentmagnets, and the permanence characteristics of said magnets, located adjacent said uniform magnetic device being proportioned relative to one another to increase the magnetic effect of magnets having fields opposed to said leakage magnetic field and decrease the magnetic effect of magnets having magnetic fields in coincidence with said leakage magnetic field in a decreasing amplitude with distance frorm said uniform magnetic device, to compensate substantially for the effects of said inherent leakage magnetic field on said periodic magnetic field.

, References Cited by the Examiner UNITED STATES PATENTS ELI LIEBERMAN, Acting Primary Examiner.

ARTHUR GAUSS, HERMAN KARL SAALBACH, Examiners. 

1. A MAGNETIC FOCUSSING SYSTEM FOR A TRAVELLING WAVE TUBE INCLUDING AN ELECTRON GUN REGION AND A DELAY LINE REGION COMPRISING: A UNIFORM MAGNETIC DEVICE FOR PRODUCING A SUBSTANTIALLY UNIFORM MAGNETIC FIELD AXIALLY THREADING SAID ELECTRON GUN REGION OF AN INSERTED TRAVELLING WAVE TUBE, SAID DEIVCE HAVING AN INHERENT LEAKAGE MAGNETIC FIELD; A PERIODIC MAGNETIC DEVICE ENCIRCLING THE DELAY LINE REGION OF SAID TUBE, HAVING A SEQUENCE OF SUCCESSIVELY OPPOSITELY DIRECTED ANNULAR PERMANENT MAGNETS OF EQUAL MAGNETIC STRENGTH AND RADIAL POLE PIECES ARRANGED BETWEEN RESPECTIVE PAIRS OF NEIGHBORING OF SAID MAGNETS, EACH OF SAID POLE PIECES HAVING AN ANNULAR AXIAL SEGMENT, SAID SEGMENTS BEING OF SUBSTANTIALLY EQUAL LENGTH AND BEING FIXEDLY POSITIONED RELATIVE TO SAID POLE PIECES TO PROVIDE DIFFERENT AXIAL SEPARATIONS BETWEEN ADJACENT SUCCESSIVE PAIRS OF SAID AXIAL SEGMENTS SUCH THAT THE MAGNETIC EFFECT OF MAGNETS HAVING MAGNETIC FIELDS OPPOSED TO SAID LEAKAGE FLUX WILL BE INCREASED AND THE MAGNETIC EFFECT OF MAGNETS HAVING MAGNETIC FIELDS IN COINCIDENCE WITH SAID LEAKAGE MAGNETIC FIELD WILL BE DECREASED, THE DIFFERENCE IN SAID SEPARATION BETWEEN ADJACENT SUCCESSIVE PAIRS OF SEGMENTS DECREASING WITH DISTANCE FROM SAID UNIFORM MAGNETIC DEVICE TO COMPENSATE SUBSTANTIALLY FOR THE EFFECTS OF SAID INHERENT LEAKAGE MAGNETIC FIELD ON SAID PERIODIC MAGNETIC FIELD. 